ffmpeg -r 3 -i D:\Tmp\tmpanim\%03d.png -vcodec huffyuv -pix_fmt rgba out.avi

ffmpeg version N-39877-g4fa706a Copyright (c) 2000-2012 the FFmpeg developers
  built on Apr 16 2012 14:53:47 with gcc 4.6.3
  configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-ru
ntime-cpudetect --enable-avisynth --enable-bzlib --enable-frei0r --enable-libass
 --enable-libcelt --enable-libopencore-amrnb --enable-libopencore-amrwb --enable
-libfreetype --enable-libgsm --enable-libmp3lame --enable-libnut --enable-libope
njpeg --enable-librtmp --enable-libschroedinger --enable-libspeex --enable-libth
eora --enable-libutvideo --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-
libvorbis --enable-libvpx --enable-libx264 --enable-libxavs --enable-libxvid --e
nable-zlib
  libavutil      51. 46.100 / 51. 46.100
  libavcodec     54. 14.101 / 54. 14.101
  libavformat    54.  3.100 / 54.  3.100
  libavdevice    53.  4.100 / 53.  4.100
  libavfilter     2. 70.100 /  2. 70.100
  libswscale      2.  1.100 /  2.  1.100
  libswresample   0. 11.100 /  0. 11.100
  libpostproc    52.  0.100 / 52.  0.100
Input #0, image2, from 'D:\Tmp\tmpanim\%03d.png':
  Duration: 00:00:01.00, start: 0.000000, bitrate: N/A
    Stream #0:0: Video: png, rgba, 64x64, 3 fps, 6 tbr, 3 tbn, 3 tbc
File 'out.avi' already exists. Overwrite ? [y/N] y
Incompatible pixel format 'rgba' for codec 'huffyuv', auto-selecting format 'bgr
a'
[buffer @ 03d05ae0] w:64 h:64 pixfmt:rgba tb:1/1000000 sar:0/1 sws_param:flags=2

[buffersink @ 03d3fa80] auto-inserting filter 'auto-inserted scale 0' between th
e filter 'src' and the filter 'out'
[scale @ 03d3fe40] w:64 h:64 fmt:rgba sar:0/1 -> w:64 h:64 fmt:bgra sar:0/1 flag
s:0x4
Output #0, avi, to 'out.avi':
  Metadata:
    ISFT            : Lavf54.3.100
    Stream #0:0: Video: huffyuv (HFYU / 0x55594648), bgra, 64x64, q=2-31, 200 kb
/s, 6 tbn, 6 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (png -> huffyuv)
Press [q] to stop, [?] for help
frame=    3 fps=0.0 q=0.0 Lsize=      25kB time=00:00:00.83 bitrate= 246.9kbits/
s
video:19kB audio:0kB global headers:0kB muxing overhead 29.138208%